Field of the Invention
This invention relates to treatment of waste water and, more particularly, to novel systems and methods for heavy metals removal from a waste water stream.
Background Art
Prior art systems exist for various types of waste water treatment. For example, recycling waste water from sewage systems in cities is classic and well established. Moreover, production water from petroleum production and coal-bed methane production is also well established.
Typically, removal of heavy metals in particular is accomplished in a vat or tank dedicated to an electrochemical, water treatment process. In this process, conventional systems focus on a balance between problems. For example, fouling occurs as a result of flocculation and precipitant accumulation on electrodes and other reactive surfaces. Engineers balance between throughput or flow rate of waste water treated and efficiency measured with respect to the amount of surface area available on reaction plates, and so forth.
Typically, maintenance is excessive in many designs. In fact, much of the prior art is dedicated to the issue of maintenance of systems particularly with regard to cleaning off reaction plates (electrodes). Various deposits may accumulate as a direct result of chemical reactions in the waste water treated and the electrical activity near the electrode.
As a practical matter, maintenance, and particularly cleaning of electrode plates, is at the center of much of the prior art literature and accepted as a given, or requirement. It is simply inescapable, due to the nature of the processes occurring in the reactor tank. For example, an electrochemical reaction occurs at each of two electrodes. Typically, a sacrificial anode or simply an anode will donate positive current (draw electrons) in order to generate certain ions.
At an opposite, cathodic, electrode, electrons are donated to ions, such as ions of hydrogen. This generates hydrogen gas as a byproduct of the freeing up of ions for reaction in the tank. The release of hydrogen and formation of hydrogen ions into hydrogen gas are a direct result of balancing the electrochemical reaction. Stated another way, the balanced half reaction of the hydrogen necessarily involves acceptance of electrons and formation of the hydrogen gas.
Another aspect of the prior art is the attention to certain electrical schemes created for the purpose of interference with, reduction of, or reversal of the plating out or coating of undesirable materials over electrodes. Coating of electrodes tends to interfere with their effectiveness, system efficiency, and so forth. As a practical matter, reversing polarity between electrodes is a common approach to reversing the coating process.
Nevertheless, it has been found by the inventors that such coating processes are not necessarily reversible. In fact, they tend to resist reversal, and require effectively undercutting the coating in order to remove it. In other words, the coating often becomes an effective dielectric or insulation barring free flow of electrons in the reactions at the electrodes.
In other prior art systems, the generation of hydrogen bubbles, and their natural tendency to rise, are relied upon as an agitation source to scrub or remove coatings from surfaces. As a practical matter, due to boundary layer theory of fluids, these actually tend to simply disrupt the formation process, and are largely ineffective, for actually removing deposits that have already been deposited on an electrode.
In short, myriad schemes for manipulating polarities, cycle times, frequencies, and the like exist in the prior art. Regardless of attempts to optimize surface areas, optimize resistance to coating by insulating reaction products, minimize fouling by flocculating compositions, and the like have largely been effective only in slowing the process of coating, and not effectively eliminating extensive maintenance operations and costs. Thus, what is needed is a system that operates with a minimum of maintenance. In fact, it would be a great advance in the art to provide an electrochemical reaction system that is effectively self cleaning, resistant against coating of electrodes, or both. It would be a further advance in the art to remove the common practice of de-rating systems according to their actual capacity compared to their engineered capacity.
Moreover, their capacity over time degrades far below their initial capacity. For example, the frequent and necessary process of maintenance or disassembly for cleaning is so ubiquitous that systems are de-rated so that they may be properly sized by being over-designed. This effectively amounts to reducing the expectations of performance in place to comport with reality. Between actual disassembly for cleaning at periodic times, the intervening performance degradation must be properly accommodated.
Thus, it would be a great advance in the art to provide a system that had a consistent, high fraction of available operational time. It would be a further advance to effectively eliminate routine cleaning if possible.
If possible, it would be a great advance in the art to relegate maintenance to replacement of consumed sacrificial anodes, in due course, rather than cleaning those or other electrodes. It would be another advance in the art to develop a process for design of a system that operates within a set of operational parameter values that effectively preclude cleaning as a requirement.
It would be another advance in the art to develop a process for design, and a system so designed, that result in uniform sacrificial donation of ions from a surface of a sacrificial anode.
It would be an advance to provide a consistent measure of efficiency over time and predictability of replacement.
It would be another advance in the art to create a system, and a method for designing systems, that would be responsive to variations in the incoming waste water treated. For example, different petroleous formations have inherent geological differences, resulting in different chemistries for the surrounding water or production water. Thus, waste water treatment may be subject to large variations in the constitution of heavy metals and other constituents such as dissolved solids, salinity, and the like. Accordingly, it would be an advance in the art to provide a system and a method for designing systems that can be responsive to changes in the constitution of incoming waste water without altering the reduced maintenance, operational efficiency, and so forth.
Another advance in the art would be to provide an increased efficiency of precipitation of heavy metal compositions separated out from the waste water stream. In this regard, it would be a further advance in the art to provide a system for designing a predictable performance of precipitation of the extracted materials. This may be expressed as a precipitation efficiency of a system.